1.Technical Field
The present disclosure relates to a method of applying an electrically conductive heating element to a surface of a rim of a steering wheel, and more particularly, to a method of applying an electrically conductive heating element to an entire surface of a rim of a steering wheel in order for a user to hold the rim without any temperature discomfort in winter, particularly applying an electrically conductive connection element into a space between molding materials constituting the rim to electrically connect heating elements of the molding materials.
2.Related Art
A rim of a steering wheel is a driver-manipulated element of a steering system of a vehicle. In this regard, many studies have been conducted to improve its esthetic appearance, convenience of holding, use of functional elements therewith, etc.
In particular, when starting to drive a vehicle in winter, the temperature of a rim of a steering wheel is lower than that of the human body, which affects the driver and might cause a safety problem. Accordingly, various apparatuses for heating a rim of a steering wheel to a temperature higher than that of the human body have been studied.
In a conventional technique for heating a rim of a steering wheel, as disclosed in Korean Utility Model Application No. 1989-0020599, Korean Patent Application No. 1992-0000945, and Korean Utility Model Application No. 1996-16958, heating coils 3 are buried in a rim portion 10 of a steering wheel, as shown in FIG. 1.
In order to bury the heating coils 3, as shown in FIG. 2, an insulating covering material 2 is coated around a core 1 and the heating coils 3 are bonded to an outer circumferential surface of the insulating covering material 2. Next, a surface of the rim portion 10 is finished by using a finishing member 4 such as a synthetic resin.
It is difficult to adopt the heating coils 3 that are heating elements if a steering wheel 100, as shown in FIG. 3, employs an aesthetic decoration element such as a leather 101. That is, an outer circumferential surface of the steering wheel 100 is surrounded by the leather 101 in order to improve the appearance of the steering wheel 100. In this case, the leather 101 is cut into small pieces in order to minimize loss of the leather 101 and then the small pieces are sewed, thereby inevitably producing seamed portions.
As shown in FIG. 4, a seamed portion 101a of the leather 101 protrudes because two pieces overlap to increase a thickness of the leather 101, thereby making it uncomfortable to handle the steering wheel 100.
In order to solve this problem, as shown in FIG. 5, a processing groove 105 for processing the seamed portion 101a is formed in a rim 110.
When heating coils are buried in the rim 110, however, it is difficult to electrically connect the heating coils due to the processing groove 105.
Also, in order to further improve the appearance of the steering wheel 100, as shown in FIG. 6, a section is formed of a first molding material 102 such as urethane foam and finished with the leather 101 that is genuine leather, and a remaining section is formed of a second molding material 103 such as acrylonitrile butadiene styrene (ABS) or rigid urethane and processed to have a pattern 106 such as a wood pattern, a hair pattern, or a marble pattern by using a hydraulic transfer method.
Even in this case, like in FIG. 5, a processing groove for processing end portions of the leather 101 is formed, thereby making it difficult to electrically connect the buried heating coils.
In particular, the processing groove of FIG. 6 has a depth that is 2 times or more greater than the processing groove 105 for processing the seamed portion 101a of the leather 101 of FIG. 5 because the processing groove of FIG. 6 has to have a depth great enough to maintain an adhesive force of an adhesive 107 that is used to finish the leather 101. Also, the processing groove of FIG. 6 has a width that is about ½ of that of the processing groove 105 for processing the seamed portion 101a of the leather 101 of FIG. 5 because two pieces of the leather 101 are inserted into the processing groove 105 for finishing the leather 101 of FIG. 5 whereas one piece of the leather 101 is inserted into the processing groove for distinguishing the first and second molding materials 102 and 103 of FIG. 6. Accordingly, it is more difficult to bury heat generating elements in the rim 110 including the processing groove of FIG. 6 than in the rim 110 including the processing groove 105 of FIG. 5.
Also, heating elements may be formed by, instead of burying heating coils in the rim 110, applying a conductive coating material to a surface of the steering wheel 100 by using a spray method or printing a conductive coating material onto a surface of the steering wheel 100 by using a pad printing method and then drying the conductive coating material. If the spray method is used, a coating film 120 may have a smaller thickness at the processing groove 105, and if the pad printing method is used, the inside of the processing groove 105 may not be printed.
That is, as shown in FIG. 7, the coating film 120 may have a greater thickness (A) around an edge portion of the processing groove 105 because the conductive coating material is attracted around an edge portion of the processing groove 105 due to surface tension, or may have a less thickness (B) at the edge portion of the processing groove 105 due to electrostatic induction. Accordingly, electric charges may not smoothly flow through the processing groove 105, and the conductive coating material may peel off in a subsequent process such as a process of surrounding the leather 101.
Also, if the coating film 120 is formed on the processing groove 105 by using the spray method, bubbles may be generated, thereby leading to poor flow of electric charges and irregularity in the thickness of the coating film 120.